Soils hit hard by fire and logging
Research shows the impact is much greater than we feared. Tanya Loos reports.
Forest soils need up to 80 years to recover from fires and at least 30 years to recover from logging, far longer than previously thought, Australian research has revealed.
A team led by Elle Bowd from Australian National University compared the soil health of various aged stands of mountain ash (Eucalyptus regnans) forest, and the fire and logging history of these stands.
The findings are published in a paper published in the journal Nature Geoscience.
The above ground ecology of mountain ash forest was known to be adversely affected by these twin disturbances, but until now the soils had not been studied.
“We discovered that both natural and human disturbances can have incredibly long-lasting effects on forest soils that could impact plant communities and ecosystem function,” says Bowd.
Previously, researchers had estimated a recovery time more in the order of 10 to 15 years.
The study involved collecting 729 soil cores from 81 sites of mountain ash forest in the Australian state of Victoria that were subject to various disturbance histories. Cores were analysed for a range of ecologically important measures at various depths, including available phosphorus and nitrate.
Bowd and her colleagues found that the sites subject to a combination of pressures fared the worst. Those that had histories of multiple bushfires combined with clear-cut logging or post-fire salvage logging had the lowest values of soil measures across the sites, relative to long-undisturbed sites.
“Soil temperatures can exceed 500 degrees Celsius during high-intensity fires and can result in the loss of soil nutrients” Bowd explains.
“Logging can expose the forest floor, compact soils and alter soil structure, reducing vital soil nutrients. These declines are more severe in areas that have experienced multiple fires and logging.”
David Lindenmayer, also from ANU, adds that “almost 99 per cent of Victoria’s mountain ash forests have either been logged or burnt in the past 80 years, so these forests are facing a huge uphill battle to restore themselves to their former glory”.
Carbon sequestration by forests and their soils around the world are threatened by increasing intensity and frequency of bushfires. The researchers recommend limiting clear cut and salvage logging wherever possible, particularly in previously disturbed forest ecosystems.